A safety and emergency driving method and an arrangement for performing the method is described in U.S. Pat. No. 4,791,900, and this application is incorporated herein by reference.
As described in U.S. Pat. No. 4,791,900, the brake light signal, that is, the switching on and off of the brake lights upon depression of the brake pedal, is processed in the safety system as an additional or standby signal indicating idling control, that is, a reduction of the injected fuel quantity to the idling quantity for the purpose of using the engine as a brake.
In the event of a fault such that an idle running signal FFR-LL is not produced when the accelerator pedal is completely released, a too-large an injected fuel quantity can be switched off by actuating the brakes. However, this brings with it the danger that, in the event of the brake light switch being defective in that it remains closed, it can lead to a reduction of the injected fuel quantity in critical driving situations, for example, during passing another vehicle. Also, upon actuation of the brakes and operation of the diagnosis switch of the fault memory in the EDC, fault diagnosis and removal of the fault become more difficult.
U.S. Pat. No. 4,791,900 discloses a safety arrangement wherein is detected when, in the presence of a redundant idle signal LL*, the control rod assumes a position which does not correspond to its idle position. In this case, an emergency operation is initiated. A system having a driving-speed controller FGR and a braking signal are applied to form the redundant idle-running signal. In addition, the driving-speed controller must be switched off in the presence of a brake signal.
With such an arrangement, the situation can develop that the brake switch malfunctions, that is, the switch issues a braking signal which indicates a non-actuated brake pedal even though the brake is actuated or it indicates an actuation of the brake pedal even though the brake is not actuated. In this way, the situation can develop that the driving-speed controller FGR is not switched off when the brake is actuated. This condition is to be prevented. Furthermore, an emergency driving program can under some circumstances be activated wherein there is a reduction of the quantity of fuel even though the preconditions for this condition are not present.